This year's top NBA Draft pick, in foul trouble throughout the second half, made 6-of-9 shots from the floor, 3-of-5 from 3-point range, with five rebounds, two assists, two steals and a blocked shot over 23 minutes in his first NBA contest.
"It was a lot of emotion. It would have been perfect to win," said Wembanyama. "Tonight really marks the beginning. It's still a dream, I hope to keep that dream feeling."
Slovenian guard Doncic had 33 points, 14 rebounds and 10 assists for the Mavericks, who scored the last eight points for the victory.
"It all starts with our defence," Doncic said. "We played good defence for three quarters but especially at the end we locked in."
Wembanyama, the 19-year-old phenomenon considered the top NBA prospect since LeBron James, used his 7-foot-4 (2.24m) frame, surprising quickness and outside shooting touch to display his arsenal of skills in the first game of his rookie campaign.
"I was happy. It's representative," Wembanyama said of his performance. "This in itself is not exceptional. But I hope what I do next will make it special."
Wembanyama had two fouls in the first quarter, two more early in the third quarter and his fifth only 26 seconds into the fourth quarter.
"Maybe I wanted to do too well, not to put my energy into the right things," he said. "I don't need to put that much energy into defence. I'm learning for a first game. These are simple things."
He returned with 7:12 to play and sparkled late. Wembanyama made an alley-oop dunk shot off a pass from Devin Vassell, added a 3-pointer, and his dunk with 4:56 to play gave the Spurs a 113-112 lead.
A Wembanyama jumper tied it at 115-115 with 3:55 remaining, but "Wemby" wasn't a main scoring option late for the Spurs and the Mavs were too tough down the stretch.
"I was just focused on being the best I can be when I step back in the court," Wembanyama said. "We're hungry already for the next game."
"Wemby" began drawing huge cheers from a sellout crowd after only 38 seconds, blocking a jump shot by eight-time NBA All-Star guard Kyrie Irving.
Wembanyama grabbed his first rebound off the defensive boards after 59 seconds and his first assist came 12 seconds later off a Zach Collins jumper.
Wembanyama opened his NBA scoring account on a 3-pointer with 8:24 remaining in the first quarter for a 13-7 Spurs lead.
"Fortunately for us he's a very tooled, prioritised young man," Spurs coach Gregg Popovich said of Wembanyama. "I don't have to teach him what is it to be a pro."
Tatum leads Boston win
In other NBA openers, Jayson Tatum had 34 points and 11 rebounds while Latvian forward Kristaps Porzingis added 30 points to lead Boston's 108-104 triumph at New York. Porzingis had the most points for any player making his Celtics debut.
Sacramento's Harrison Barnes scored 33 points to power Sacramento over host Utah 130-114.
Shai Gilgeous-Alexander's 31 points led Oklahoma City to a 124-104 win at Chicago.
Donovan Mitchell's 3-pointer with 12.1 seconds remaining lifted Cleveland to a 114-113 victory at Brooklyn. Mitchell and Max Strus each scored 27 to lead the Cavaliers.
Detroit missed four shots in the last 64 seconds and host Miami, led by Bam Adebayo's 22 points and 19 from Jimmy Butler, edged the Pistons 103-102.
C.J. McCollum had 24 points and Zion Williamson added 23 to lead New Orleans over host Memphis 111-104.
